1. Field
The subject invention relates to a waveguide cavity antenna for a reflector dish and the combination of the waveguide cavity antenna and reflector dish.
2. Related Art
Various antennas are known in the art for receiving and transmitting electromagnetic radiation. Physically, an antenna consists of a radiating element made of conductors that generate radiating electromagnetic field in response to an applied electric and the associated magnetic field. The process is bi-directional, i.e., when placed in an electromagnetic field, the field will induce an alternating current in the antenna and a voltage would be generated between the antenna's terminals or structure. The feed network, or transmission network, conveys the signal between the antenna and the transceiver (source or receiver). The feeding network may include antenna coupling networks and/or waveguides. An antenna array refers to two or more antennas coupled to a common source or load so as to produce a directional radiation pattern. The spatial relationship between individual antennas contributes to the directivity of the antenna.
While the antenna disclosed herein is generic and may be applicable to a multitude of applications, one particular application that can immensely benefit from the subject antenna is the reception of satellite television (Direct Broadcast Satellite, or “DBS”). In DBS, reception is accomplished with a directional antenna aimed at a geostationary satellite. In the standard DBS design, a reflector dish is coupled with one or more antenna feeds, known as feedhorns, each of the feedhorns situated so as to receive reflected signals from the reflector dish corresponding to one of the geostationary satellites. The feedhorn utilizes a waveguide structure with a horn-shaped extension. Each feedhorn is dedicated to a specific angular location in the sky—the angular location is controlled by the lateral movement (i.e., vertical or horizontal movement to correspond to each specific angular location in the sky) of the horn-shaped extension with respect to the focal point of the reflector dish.
A reflector antenna may have multiple feeds, each feed corresponding to a specific band of frequency, such as the Ku band or the Ka band or portions thereof, coming from a specific satellite, or multiple satellites. Depending on the position of the satellites in space, the corresponding feeds may have to be ideally located very close to each other. Ideal positions of multiple feeds may even overlap each other if multiple feeds are coupled to a common reflector dish. In order to physically accommodate the multiple feeds with respect to the common reflector dish, each of the feeds may be positioned at a location close to, but not exactly coinciding with the focal point of the reflector dish. Thus, received signal quality may be degraded based on the distance of a feed from the ideal focal point associated with a specific focal length to diameter ratio (f/d ratio) of the dish.